From: Tom Lane <tgl@sss.pgh.pa.us>
To: neeraj kumar <neeru.cse@gmail.com>
cc: Jeremy Schneider <schnjere@amazon.com>, pgsql-admin@postgresql.org,
        pgsql-general@postgresql.org
Subject: Re: Query on pg_stat_activity table got stuck
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Comments: In-reply-to neeraj kumar <neeru.cse@gmail.com>
	message dated "Thu, 09 May 2019 16:35:37 -0700"
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Date: Thu, 09 May 2019 23:25:01 -0400
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neeraj kumar <neeru.cse@gmail.com> writes:
> We got more information about this issue. There is one backend process
> still present into beentry which has changecount as odd value. However this
> process is long gone/terminated. It means when this process was
> killed/terminated its entry was not cleaned from beentry list. There seems
> to be some shutdown hook which cleans beentry if process is
> killed/terminated that somehow was not kicked off ?

No, that's the point: there isn't any such cleanup code.  The design
idea here was that we'd only have short straight-line code segments
with no possible way to throw an error while changecount is odd.
Then somebody abused the heck out of that ...

			regards, tom lane